Disease and Its Causes

by W. T. Councilman

The pain in an inflamed part is due to a number of factors, but chiefly to the increased pressure upon the sensory nerves caused by the exudate. The pain varies so greatly in degree and character that parts which ordinarily have little sensation may become exquisitely painful when inflamed. The pain is usually greater when the affected part is dense and unyielding, as the membranes around bones and teeth. The pain is often intermittent, there being acute paroxysms synchronous with the pulse, this being due to momentary increase of pressure when more blood is forced into the part at each contraction of the heart. The pain may also be due to the direct action of an injurious substance upon the sensory nerves, as in the case of the sting of an insect where the pain is immediate and most intense before the exudate has begun to appear.

When an inflamed area is examined, after twenty-four hours, by hardening the tissue in some of the fluids used for this purpose and cutting it into very thin slices by means of an instrument called a microtome, the microscope shows a series of changes which were not apparent on naked eye examination. The texture is looser, due to the exudate which has dilated all the spaces in the tissue. Red and white corpuscles in varying numbers and proportions infiltrate the tissue; all the cells which belong to the part, even those forming the walls of the vessels, are swollen, the nuclei contain more chromatin, and the changes in the nuclei which indicate that the cells are multiplying appear. The blood vessels are dilated, and the part in every way gives the indication of a more active life within it. There are also evidences of the tissue injury which has called forth all the changes which we have considered. (Fig. 15.)

Fig. 15—A Section Of An Inflamed Lung Showing The Exudate Within The Air Spaces. Compare this with Fig 6. Fig 15 is from the human lung, in which the air spaces are much larger than in the mouse.

The microscopic examination of any normal tissue of the body shows within it a variable number of cells which have no intimate association with the structure of the part and do not seem to participate in its function. They are found in situations which indicate that these cells have power of active independent motion. In the inflamed tissue a greatly increased number of these cells is found, but they do not appear until the height of the process has passed, usually not before thirty-six or forty-eight hours after the injury has been received. The numbers present depend much upon the character of the agent which has produced the injury, and they may be more numerous than the ordinary leucocytes which migrate from the blood vessels.

All these changes which an injured part undergoes are found when closely analyzed to be purposeful; that is, they are in accord with the conditions under which the living matter acts, and they seem to facilitate the operation of these conditions. It has been said that the life of the organism depends upon the coördinated activity of the living units or cells of which it is composed. The cells receive from the blood material for the purpose of function, for cell repair and renewal, and the products of waste must be removed. In the injury which has been produced in the tissue all the cells have suffered, some possibly displaced from their connections, others may have been completely destroyed, others have sustained varying degrees of injury. If the injury be of an infectious character, that is, produced by bacteria, these may be present in the part and continue to exert injury by the poisonous substances which they produce, or if the injury has been produced by the action of some other sort of poison, this may be present in concentrated form, or the injury may have been the result of the presence of a foreign body in the part. Under these conditions, since the usual activities of the cells in the injured part will not suffice to restore the integrity of the tissue, repair and cell formation must be more active than usual, any injurious substances must be removed or such changes must take place in the tissue that the cell life adapts itself to new conditions.

Fig. 16—Phagocytosis. a, b, c are the microphages or the bacterial phagocytes. (a) Contains a number of round bacteria, and (b) similar bacteria arranged in chains, and (c) a number of rod-shaped bacteria (d) Is a cell phagocyte or macrophage which contains five red blood corpuscles.

All life in the tissues depends upon the circulation of the blood. There is definite relation between the activity of cells and the blood supply; a part, for instance, which is in active function receives a greater supply of blood by means of dilatation of the arteries which supply it. If the body be exactly balanced longitudinally on a platform, reading or any exercise of the brain causes the head end to sink owing to the relatively greater amount of blood which the brain receives when in active function. The regulation of the blood supply is effected by means of nerves which act upon the muscular walls of the arteries causing, by the contraction or the relaxation of the muscle, diminution or dilatation of the calibre of the vessel. After injury the dilatation of the vessels with the greater afflux of blood to the part is the effect of the greatly increased cell activity, and is a necessity for this. In many forms of disease it has been found that by increasing the blood flow to a part and producing an active circulation in it, that recovery more readily takes place and many of the procedures which have been found useful in inflammation, such as hot applications, act by increasing the blood flow. So intimate is the association between cell activity, as shown in repair and new formation of cells, and the blood flow, that new blood vessels frequently develop by means of which the capacity for nutrition is still more increased. The cornea or transparent part of the eye contains no blood vessels, the cells which it contains being nourished by the tissue fluid which comes from the outside and circulates in small communicating spaces. If the centre of the cornea be injured, the cells of the blood vessels in the tissue around the cornea multiply and form new vessels which grow into the cornea and appear as a pink fringe around the periphery; when repair has taken place the newly formed vessels disappear.

The exudate from the blood vessels in various ways assists in repair. An injurious substance in the tissue may be so diluted by the fluid that its action is minimized. A small crystal of salt is irritating to the eye, but a much greater amount of the same substance in dilute solution causes no irritation. The poisonous substances produced by bacteria are diluted and washed away from the part by the exudate. Not only is there a greater amount of tissue fluid in the inflamed part, but the circulation of this is also increased, as is shown by comparing the outflow in the lymphatic vessels with the normal. The fluid exudate which has come from the blood and differs but slightly from the blood fluid exerts not only the purely physical action of removing and diluting injurious substances, but in many cases has a remarkable power, exercised particularly on bacterial poisons, of neutralizing poisons or so changing their character that they cease to be injurious.